1. Field of the Invention
The present invention relates to a frequency triplicator for microwaves, in particular for microwaves with input frequencies above about 30 GHz to for example about 100 or 200 GHz.
Microwave radiation of high power is required for example for heating fusion plasmas. With the present microwave generators, for example gyrotrons, about 200 kW can be generated at about 70 GHz. However, microwave radiation of still higher frequency is required, for example up to 300 GHz and more, to be able to effectively heat plasmas with a higher electron density than hitherto. The development of transmission tubes for such high frequencies becomes increasingly difficult the higher the frequency because for example in gyrotrons increasingly higher magnetic fields are required and in addition the mechanical tolerances become increasingly more critical with decreasing wavelength.
2. Description of the Related Art including information disclosed under 37 CFR .sctn..sctn.1.97-1.99
From a publication by K. Seeger, J. Appl. Phys. 34, No. 6, June 1963, p. 1608-1611, it is known to triple the frequency of electromagnetic oscillations having a frequency of about 10 GHz by means of a nonlinear material, i.e. n-germanium with a resistivity of 5.5 ohm.multidot.cm. The maximum efficiency, i.e. the ratio of output power in the triple frequency to input power in the fundamental frequency, was only about 0.95% and at the end of said publication it is stated that the power of the third harmonic generated decreases with increasing frequency. From a publication of A. Mayer and F. Keilmann, Physical Review B, 33, No. 10, May 15, 1986, p. 6962-6968, it is known that in the far infrared region frequency triplication can be achieved with the aid of doped semiconductor materials such as Ge, Si and GaAs, and an efficiency of 10.sup.-3 was measured.